1. Field of the Invention
The present invention relates generally to vacuum pumps and, more specifically, to a turbo-molecular pump used to discharge process gas of a semiconductor manufacturing apparatus.
2. Description of the Related Art
As a result of the rapid progress in techniques for manufacturing semiconductors for an integrated circuit or the like and the demand for higher production amounts thereof, there is an increasing demand for a vacuum pump for discharging process gas from the chamber of a semiconductor manufacturing apparatus.
Generally speaking, as such a vacuum pump, a turbo-molecular pump in which the exhaust amount per unit time is large and which makes it possible to attain a high vacuum is used.
The exhaust system for discharging gas from the chamber of a semiconductor manufacturing apparatus is formed by arranging piping directly below the chamber to connect a conductance valve, and connecting a turbo-molecular pump to the conductance valve. The conductance valve is a valve for adjusting the chamber pressure.
By thus arranging the turbo-molecular valve in close vicinity to the chamber, the piping from the chamber to the turbo-molecular pump is shortened, whereby the reduction in conductance (easiness with which exhaust gas is conveyed) due to the piping is restrained.
In some cases, the turbo-molecular pump is directly connected to the chamber of the semiconductor manufacturing apparatus, without providing any conductance valve therebetween.
In the chamber of the semiconductor manufacturing apparatus, operations such as application of high-temperature process gas in the form of plasma to a semiconductor substrate and etching thereon are performed.
Such process gas is discharged by the turbo-molecular pump through the conductance valve, without being sufficiently cooled.
Thus, heat is imparted to the piping connected to the chamber and the conductance valve, and this heat is transmitted to the turbo-molecular pump.
In some cases, to enhance the reactivity of the process gas, the chamber itself is heated. Further, nowadays, in some cases, to prevent generation of deposit of the product, the conductance valve is heated.
As a result of heat conduction due to these factors, the temperature of the flange portion formed in the inlet of the turbo-molecular pump can exceed 60xc2x0 C.
Inside a turbo-molecular pump, a rotor having a large number of radially arranged rotor blades rotates at a high speed of approximately several tens of thousand rpm.
The rotor blades are formed by an aluminum alloy or the like, which is superior in mechanical strength and lightweight.
However, the permissible temperature of the rotor blades is relatively low, ranging, for example, from 120xc2x0 C. to 150xc2x0 C. When the turbo-molecular pump is used for a long period of time at a temperature higher than this permissible temperature, the rotor blades undergo creep deformation due to the centrifugal force caused by high-speed rotation, resulting in a breakdown and a rather short period until parts replacement.
Further, when the flow rate of the exhaust gas is high, the temperature of the rotor blades, etc. rises due to collision of the molecules constituting the gas with the rotor blades and friction therebetween, so that, in some cases, to use the turbo-molecular pump at a temperature not higher than the permissible temperature, the amount of exhaust gas that can be continuously allowed to flow through the turbo-molecular pump (permissible flow rate) is limited.
It is accordingly an object of the present invention to provide a vacuum pump whose temperature rise is restrained, whereby deterioration in the vacuum pump due to temperature rise does not easily occur.
To achieve the above object, there is provided, in accordance with the present invention, a vacuum pump characterized by comprising a casing constituting an armor body, a gas inlet formed in the casing and connected to a container to be evacuated, a gas outlet formed in the casing, an exhaust means which sucks in a gas through the gas inlet and discharges the gas sucked in through the gas inlet through the gas outlet, and a bad heat conductor arranged in an end surface of the gas inlet (First Construction).
In the first construction, the gas inlet may be equipped with a flange, and the bad heat conductor may consist of a coating or plating formed on an opening surface of the flange (Second Construction).
Further, the bad heat conductor in the first construction may be a tubular member one end of which is connected to the gas inlet and the other end of which is connected to the container to be evacuated (Third Construction). The bad heat conductor in one of the first through third constructions may consist, for example, of a ceramic, resin, glass, or metal of low heat conductivity.
Further, in accordance with the present invention, there is provided a vacuum pump comprising a casing constituting an armor body, a gas inlet formed in the casing and connected to a container to be evacuated, a gas outlet formed in the casing, and an exhaust means which sucks in a gas through the gas inlet and discharges the gas sucked in through the gas inlet through the gas outlet, characterized in that at least a part of the casing portion from the gas inlet to the position where the exhaust means is accommodated is formed of a bad heat conductor over the entire circumference of the casing (Fourth Construction).
Further, to achieve the above object, there is provided, in accordance with the present invention, a vacuum pump characterized by comprising a casing constituting an armor body, a gas inlet formed in the casing and connected to a container to be evacuated, a gas outlet formed in the casing, an exhaust means which sucks in a gas through the gas inlet and discharges the gas sucked in through the gas inlet through the gas outlet, a good heat conductor arranged in the gas inlet, and a cooling means for cooling the good heat conductor (Fifth Construction). This good heat conductor may consist, for example, of aluminum or copper. The good heat conductor is, for example, a tubular member one end of which is connected to the gas inlet and the other end of which is connected to the container to be evacuated. The cooling means may consist of a cooling water supplying means for supplying cooling water to the periphery of the good heat conductor or a blowing means for supplying air flow to the periphery of the good conductor. When cooling the good conductor with air, it is possible to provide an air cooling fin in the periphery of the good conductor. The cooling means is not limited to the water cooling type and the air cooling type. It is also possible to use, for example, a device utilizing the Peltier effect, such as a Peltier element, and other methods.
Further, in the fifth construction, the good heat conductor is connected to the container to be evacuated through the bad heat conductor, whereby the quantity of heat transmitted from the gas inlet to the vacuum pump is reduced, and it is possible to prevent the container to be evacuated from being over-cooled by the cooling means (Sixth Construction).
In a vacuum pump according to one of the first through sixth constructions, the gas inlet is formed at one end of the casing, and the gas outlet is formed at the other end of the casing, and the exhaust means is a turbo-molecular pump including a rotor accommodated in the casing and rotatably supported, a plurality of rotor blades arranged radially in the periphery of the rotor, a driving means for driving the rotor to rotate it around the axis thereof, and a plurality of stator blades arranged from the inner peripheral surface of the casing toward the center of the casing (Seventh Construction).